1. Field of the Invention
This invention relates to melt growth of semiconductors. More specifically, the invention is a method for promoting single crystal growth during fabrication of melt growth semiconductors.
2. Description of the Related Art
Some semiconductors are melted prior to the growth of crystals therefrom. Typically, the semiconductor material is placed in an ampoule that is then heated in a furnace whereby the semiconductor melts. During cooling, crystal growth originates at the ampoule's tip. Existing bulk crystal growth apparatus/techniques (e.g., the Bridgman technique) tend to generate poor quality multi-grained crystals as the melted semiconductor undergoes supercooling. That is, the supercooling prohibits the ideal crystal growth condition in which a small single crystal nucleus forming at the ampoule's tip and subsequently grows into a large single crystal.
The large multi-grained crystal growth problem is evidenced by an analysis of melted cadmium zinc telluride semiconductor that revealed a common supercool of 40-50° C. This means that, during cooling, the melt does not solidify into a solid until it is 40-50° C. below the equilibrium solidus temperature of the material. Under a typical crystal growth process used for cadmium zinc telluride, the thermal gradient at the liquidus temperature is about 10° C. per centimeter. This implies that a solid section of about 4-5 centimeters long will be formed spontaneously at the end of supercooling. Thus, the large supercool prohibits the growth of a small single crystal nucleus that can grow into a large single crystal. Unfortunately, the real value of the cadmium zinc telluride is realized when large single crystals thereof can be fabricated.